1. Field of the Invention
The present invention relates generally to handheld pneumatic power tools, and more particularly to a handheld tool having a foot-controlled pressure regulator for controlling power to the tool.
2. Discussion of the Prior Art
It is known to provide a handheld pneumatic power tool including a handpiece having a cylinder within which a piston is provided, wherein pressurized air is supplied to the handpiece to oscillate the piston back and forth into and out of engagement with an engraving tool tip.
In this known construction, the means for oscillating the piston within the cylinder includes an air inlet for introducing pressurized air to an end of the cylinder remote from the tool tip, and a compression spring between the piston and the tool tip for biasing the piston against the pneumatic pressure. Exhaust ports communicate with the cylinder at a position intermediate the ends thereof and permit air to be exhausted from the cylinder when the piston is adjacent the tool tip. Thus, pneumatic pressure overcomes the spring to drive the piston in a first direction against the tool tip, and as air is exhausted from the cylinder, the spring biases the piston back away from the tool tip in a second direction.
Control of the handpiece is achieved by controlling the pressure of air supplied to the handpiece. In the conventional construction, this control is obtained by providing a pressure regulator between the air supply and the tool, and a foot-controlled pinch valve. The pressure regulator is normally mounted between the air supply and the pinch valve, and includes a hand-operated knob for adjusting the regulated pressure of the air supplied to the pinch valve.
In this conventional construction, the foot-controlled pinch valve restricts a passage through which air is supplied to the handpiece. Thus, to a certain extent, it is possible to manually control the size of the passage in order to control the amount of air supplied to the handpiece.
In the conventional construction, a certain minimum pressure must be supplied to the handpiece to initiate oscillation of the piston against the bias of the spring. However, this minimum start-up pressure is greater than the minimum pressure needed to maintain oscillation of the piston subsequent to start-up. In order to operate the handpiece at any given pressure below the minimum start-up pressure, it is necessary to supply a higher pressure than desired in order to start the piston oscillating, and to then back off the pressure to the desired level. Alternately, the user can shake the handpiece while supplying the desired level of pressure in the hope that the shaking motion and pressure together will initiate oscillation of the piston.
A problem encountered during use of the conventional construction is that it is often desirable to initiate oscillation of the piston with the tool tip placed against the work piece. For example, when doing intricate engraving work, the tip must be positioned on the work piece before being energized. Otherwise, it is difficult for the user to make the engraving at the desired location on the work piece. In order to obtain the desired control of air to the handpiece, it is necessary for a user of the conventional system to repeatedly adjust the hand-operated pressure regulator and to fiddle with the position of the on/off valve. This represents an inconvenience since the user must remove a hand from the work piece in order to control pressure to the handpiece.